Many different ultrasonic multi-plane probes, arranged for positioning within the body, have been suggested or put into actual use in the past. Certain of these prior art ultrasonic multi-plane probes are arranged with the ultrasonic transducer array located within a cylindrical housing. To rotate the ultrasonic transducer array of these probes, the ultrasonic transducer array is mounted upon a pulley or shaft. The pulley is directly connected to a cable which rotates the pulley and, in turn, the ultrasonic transducer array.
Some probes contain a transducer array inside of a cavity within a cylindrical housing. It is common practice in the design of these probes to fill the cavity in which the ultrasonic transducer array unit is located with a fluid or viscous acoustic coupling material, such as a grease, and to cover the cavity with a membrane or lens element. The viscous acoustic coupling material is provided in such probes to establish the acoustic coupling from the array into the membrane. The presence of the fluid in the cavity in the probe housing is the source of potential damage to the ultrasonic transducer array. The viscous coupling material is an extra element in the acoustic path and can cause attenuation and distortion of the desired signals.
Other multi-plane probes locate the ultrasonic transducer external to the base unit. Probes of this type provide direct contact between the ultrasonic transducer array and body tissue, such as the lining of the esophagus. Direct contact reduces or eliminates possible signal attenuation and distortion.
A problem with multi-plane probes of the prior art is the lack of control for accurate rotation of the transducer array to desired preset positions in order to rotate to, and maintain the transducer array at, a desired position.
A further problem with prior art ultrasonic multiplane probes is that when examining a patient's body, it is necessary to reposition the probe in the esophagus, to get the best alignment of the transducer with the organ being examined. In doing so, it is necessary to flex the probe unit cable which, in turn, causes the internal rotation control cables to move. This results in the transducer array rotating slightly, changing its alignment.